Wastewaters frequently require treatment in order to remove carried materials which could damage the environment. Alum and ferric salts such as ferric sulfate and ferric chloride, and chlorinated copperas, are well-known coagulants, particularly in waters having a pH in the acid range between 4.5 and 6.5. Ferrous salts likewise are effective coagulants in this alkaline pH range. Other known coagulants include basic halide salts of either iron or aluminum.